1. Field of the Invention
The present invention relates to a thermostat capable of performing an exposure treatment on a subject while maintaining the subject at a constant temperature. For example, the thermostat can be used in the production of a liquid crystal display device which contains a mixture of a liquid crystal material, a photopolymerizable polymer resin and the like.
2. Description of the Related Art
Conventionally, an exposure apparatus that is employed for producing a liquid crystal display device is used in a step of photolithography, a step of ultraviolet (hereinafter, simply referred to as "UV") cleaning, a step of sealing the panel, or the like. In these steps, it is not necessary to control the temperature of the panel.
Japanese Laid-Open Patent Publication No. 6-230581discloses an exposure apparatus for processing both surfaces of the subject. The exposure apparatus is capable of forming exposed patterns precisely corresponding to patterns of a pair of original films on both surfaces of the subject at the same time.
Recently, a display mode of a liquid crystal display device such as PDLC (Polymer Dispersed Liquid Crystal), which contains a liquid crystal material and a photopolymerizable polymer resin, is receiving much attention as one liquid crystal display modes. FIGS. 7A and 7B are perspective views for illustrating a method for producing a liquid crystal display device 100 having the above-described mode proposed by the present inventors. FIGS. 8A and 8B are perspective views illustrating another method for producing a liquid crystal display device 200 having the above-described mode proposed by the present inventors.
As shown in FIG. 7A, a mixture 113 of a liquid crystal material, a photopolymerizable resin and a photopolymerization initiator is injected between a pair of opposing substrates 101a and 101b. Thereafter, the upper substrate 101a is covered with a photomask 114 having light shielding portions 110 and light transmitting portions 111 such that the light shielding portions 110 cover pixel portions. Then, UV light 108 is radiated toward the mixture 113 through the photomask 114 as represented by allows in FIG. 7A. As a result, as shown in FIG. 7B, the liquid crystal display device 100 is obtained which includes a liquid crystal medium layer having pixel portions irradiated with weaker light being liquid crystal regions 106, where the liquid crystal material concentrates and regions other than the pixel regions irradiated with stronger light being polymer walls 107 where a polymer material concentrates.
According to the production process of the liquid crystal display device 100, the subject needs to be uniformly heated to a temperature equal to or higher than the temperature where the mixture undergoes a phase change to an isotropic phase state during the step of radiating UV light to the subject covered with the above-mentioned photomask, in order to enhance the compatibility of the liquid crystal material and the photopolymerizable resin etc, i.e., in order to enhance the uniformity of the mixture of the liquid crystal material and the photopolymerizable polymer resin etc. Moreover, such a temperature needs to be maintained while radiating the subject with light.
As shown in FIG. 8A, a pair of substrates 201a and 201b included in the liquid crystal display device 200 are provided with transparent electrodes 202a and 202b which hardly transmit light with a certain wavelength. Accordingly, the liquid crystal display device 200 having liquid crystal regions precisely corresponding to the profile of the pixels can be obtained without covering the liquid crystal panel of the liquid crystal display device with a photomask.
Electrodes 202a and 202b on respective substrates 201a and 201b are made of a material that hardly transmits UV light and patterned in a striped manner. The pair of substrates 201a and 201b are attached with each other such that the intersections of the electrodes 202a and 202b are arranged in a matrix. Then, the above-mentioned mixture is injected between the pair of substrates 201a and 201b, thereby forming the liquid crystal cell 200. Thereafter, the surfaces of the liquid crystal cell 200 are irradiated with UV light 208, the radiation being applied either one surface at a time or simultaneously. As a result, the regions irradiated with weaker light corresponding to pixel regions become the liquid crystal regions 106 where the liquid crystal material concentrates and the regions other than the pixel regions, which are irradiated with stronger light, become the polymer walls 107 where the polymer material concentrates (Japanese Laid-Open Patent Publication No. 7-287241). Thus, a liquid crystal display device 200 having the liquid crystal medium layer is completed.
According to the above-described method for producing the liquid crystal display device, the temperature of the liquid crystal cell needs to be maintained constant during the light radiation process. Conventionally, the light radiation treatment is performed on one surface of the subject at a time while maintaining the subject on a hot plate and, when necessary, covering an upper surface of the subject with a photomask.
However, in such a case, the upper surface of the substrate is directly exposed to the outside air, which is at a lower temperature, and thus maintaining the uniform temperature of the entire substrate is difficult. When the exposure treatment is performed in such a state, it is difficult to realize a desired phase separation. Further, there is a problem of display defects due to the uneven temperature of the surface of the subject.
Moreover, since the exposure treatment is performed on one surface of the subject at a time, there is a problem of low production efficiency.
Japanese Laid-Open Patent Publication No. 6-230581 discloses an exposure apparatus capable of exposing both surfaces of the subject at the same time. However, the above-mentioned exposure apparatus is not able to heat the subject and thus, producing the above-described display device in a satisfactory manner is very difficult.